Causes

Doctors don't know the cause of uterine fibroids, but research and clinical experience point to these factors:

Genetic changes. Many fibroids contain changes in genes that differ from those in normal uterine muscle cells. There's also some evidence that fibroids run in families and that identical twins are more likely to both have fibroids than nonidentical twins.

Hormones. Estrogen and progesterone, two hormones that stimulate development of the uterine lining during each menstrual cycle in preparation for pregnancy, appear to promote the growth of fibroids. Fibroids contain more estrogen and progesterone receptors than normal uterine muscle cells do. Fibroids tend to shrink after menopause due to a decrease in hormone production.

Other growth factors. Substances that help the body maintain tissues, such as insulin-like growth factor, may affect fibroid growth.

Frequently asked questions. Special procedures FAQ084. Hysteroscopy. American College of Obstetricians and Gynecologists. http://www.acog.org/~/media/For%20Patients/faq084.pdf?dmc=1&ts=20130507T1056219214. Accessed May 7, 2013.

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